Preloaded cushioned bearing assembly

ABSTRACT

In a bearing assembly for a steering column assembly for example, the bearing assembly comprising an axially split bearing and elastomeric crown, the crown acting to close the split, there is disclosed an improved elastomeric crown. The crown includes a plurality of passageway extending through the crown. The crown also includes a plurality of ribs extending outwardly of the crown. The improved elastomeric crown allows more constant pressure fields and low torque variations of a shaft running in the bearing.

The present invention relates to an improved bearing assembly havingprimary, though not exclusive use, as a bearing assembly for steeringcolumns for use in automotive vehicles, and to an elastomeric crown foruse in such a bearing assembly.

A steering column includes all the elements necessary to enable motionsof a steering wheel to be transmitted to a steering rack. The steeringcolumn includes a mounting tube in which a shaft, linking together thesteering wheel and the steering rack, is guided in rotation. The shaftis supported in the tube by a plurality of bearing assemblies.

When used in steering columns, bearing assemblies must satisfy a numberof conditions. Vehicle manufacturers specify the mounting, speed andtemperature conditions at which the bearing assemblies will need tooperate. The bearing assemblies must allow stresses from the steeringwheel to be transmitted via the shaft and must run silently. Further,the bearing assemblies must maintain their properties throughout theworking life of the steering column despite the various environmentalfactors encountered, including changing levels of temperature, humidityand grease.

It is known to construct bearing assemblies for this purpose comprisinga split bearing, about which is located an elastic element, the elasticelement in use being located between the bearing and a mounting tube tolocate the bearing axially in relation to the mounting tube. In this waya continuous pressure may be maintained on the rear surface of thebearing acting to close the split.

However, in known bearing assemblies, such as those described above, theforce exerted on the rear surface of the bearing will follow theintrinsic physical characteristics of the elastic element. In additionthe force exerted will be affected by any irregularities on the insidesurface of the housing. These characteristics can cause problems inobtaining and maintaining an even, or substantially even, force on therear surface of the bearing. There is a need for an elastic element tohave a substantially constant pressure on the rear surface of thebearing in order to guarantee the constancy of the rotating torquevalue. It would be an advantage for the substantially constant pressureto be at the minimum required to do this. This is because,unfortunately, in some circumstances, maintaining the substantiallyconstant pressure on the rear surface of the bearing against theopposing force exerted by the bearing will cause creep bending to occurin the elastic element. Clearly, it would be an advantage to have thelowest stress level in the elastic element to avoid creep bendingoccurring.

It is an advantage of the present invention that an elastomeric crownaccording to the present invention eliminates or substantially reducesthese problems.

According to a first aspect of the present invention, we provide anelastomeric crown for a bearing assembly comprising an elastomericcylinder having an annular wall about a longitudinal axis, a pluralityof passageways extending longitudinally through the cylinder wall and aplurality of ribs extending along an outer surface of the elastomericcylinder.

Preferably the passageways extend parallel to the longitudinal axis ofthe elastomeric element.

The cross sectional shape of the passageways may be any desired and mayinclude round, oval, hexagonal for example.

The elastomeric element is provided with a plurality of ribs extendingalong an outer surface of the elastomeric element.

More preferably the plurality of ribs extend substantially parallel tothe longitudinal axis of the elastomeric cylinder.

More preferably the plurality of ribs are located radially of thepassageways extending through the elastomeric element.

The cross sectional shape of the ribs may be any desired shape.

Preferably at least one of the plurality of ribs comprises a beadextending longitudinally along the elastomeric cylinder projecting froman outer surface of the elastomeric cylinder, the outer surface of thebead being a flat disposed parallel to a tangent of the outer surface ofthe elastomeric cylinder.

Preferably the plurality of passageways comprises twelve passageways.

According to a second aspect of the invention, we provide a bearingassembly comprising a cylindrical bearing having an axial split and anelastomeric crown according to the first aspect of the invention, theelastomeric crown being located about the split bearing.

Although the bearing assembly of the present invention is described withparticular reference to steering columns for vehicles as an example ofits use, the bearing assembly according to the present invention iseffectively a “clearance-free bearing assembly” where the bearing runsagainst a co-operating shaft without clearance due to the radiallycompressive force due to the crown. Thus, the bearing assembly of thepresent invention has many applications other than in steering columns.

According to a third aspect of the present invention, we provide asteering column assembly including at least one bearing assemblyaccording to the second aspect of the invention.

The invention will now be described, by way of example only, withreference to the accompanying drawings, in which:

FIG. 1 shows a view parallel to the axis of a bearing assembly accordingto the present invention:

FIG. 2 shows a section of the bearing assembly along line A—A of FIG. 1;

FIG. 3 shows diagrammatically the contact pressure at an inner surfaceof an elastomeric element in a first embodiment of the presentinvention;

FIG. 4 shows diagrammatically the contact pressure at an outer surfaceof an elastomeric element in a first embodiment of the presentinvention;

FIG. 5 shows diagrammatically the contact pressure at an inner surfaceof the elastomeric element in a second embodiment of the presentinvention; and

FIG. 6 which shows diagrammatically the contact pressure at an outersurface of the elastomeric element of the second embodiment of thepresent invention.

Referring first to FIGS. 1 and 2, there is shown a first embodiment ofthe present invention. A bearing assembly 1 is shown for locating ashaft 60 in a housing 62 (the shaft 60 and housing 62 are shown only inpart in FIG. 2). The bearing assembly comprises a split bearing 3 bushand elastomeric crown 4. Typically, the bearing is manufactured fromsteel strip. An inner surface 5 of the bearing 3 is lined with ananti-friction material, typically a polymer with a low surface hardness,for example PTFE, polyacetal or PEEK. The lining is able to run dry orpartially lubricated.

In its free spread state the bearing has an axial split 8 which underpressure may be closed. The peripheral length of the bearing is suchthat when the axial split is closed, the internal diameter of thebearing is less that the external diameter of the shaft. In use, theshaft 60 is inserted into the bearing pushing the bearing outwards. Atthe same time the elastomeric crown between the bearing and the housingis compressed, acting to push the bearing 3 back towards the shaft. Inthis way the bearing can be run without clearance between it and theshaft. Also, any wear in the bearing is compensated for automatically.

The elastomeric crown 4 is generally cylindrical and has an innersurface and an outer surface 20, these surfaces being joined by a firstend face 13 and a second end face 14. Each of the end faces is formedwith a shoulder 17 to form a recess 21 on each side of the elastomericcrown 4. The recesses 21 define an inner portion 9 of the elastomericcrown.

The bearing 3 is provided with two flanges 6, 7 which extend radiallyoutward. The flanges 6, 7 embrace the inner portion 9 of the elastomericcrown 4 to prevent relative axial movement of the crown and the bearingoccurring during use of the bearing assembly. The recesses 21 are ofsufficient depth such that in use the flanges 6, 7 of the bearing sitcomfortably within the recesses 21, and do not extend beyond the planesof the first and second end faces 13, 14 of the elastomeric crown.Relative rotational movement of the bearing 3 and the elastomeric crown4 is prevented due to the high level of friction between the two parts.

The elastomeric crown 4 is also provided with a plurality of passageways11 The plurality of passageways 11 are formed in the elastomeric crownas part of the manufacture of the elastomeric crown 4 by moulding. Inthe embodiment illustrated in FIG. 1 there are twelve such passageways.Each of the passageways 11 extend from the first end face. 13 of theelastomeric crown to the second end face 14. In the embodiment shown,each of the passageways has a longitudinal axis 12 extendingsubstantially parallel to a longitudinal axis 10 of the elastomericcrown. Each of the passageways 11 is located between the inner portionof the crown extending between the flanges 6, 7 and an outer surface 20of the elastomeric crown. More precisely, the axis 12 of each passageway11 is located radially within the start of the shoulder 17 forming therecess 21 in each end face 13, 14. Each of the passageways 11 is locatedin order that in use the passageway is located radially outward of theflanges 6, 7 of the bearing 3.

Each of the passageways is of substantially uniform cross-section alongits width. In the embodiment shown, each of the passageways is ofgenerally circular cross-section when the elastomeric crown is in anunstressed condition. Each of the passageways 11 is locatedcircumferentially equidistantly from one another. Dividing the crownaxially into accurate portions defined by those portions that contain apassageway and those that do not contain a passageway, it can be seenthat in this embodiment, such portions are equal to one another.

The elastomeric crown 4 is further provided with a plurality of ribs 15located about the periphery of the outer surface 20 of elastomeric crown4. Each of the plurality of ribs runs from the first end face 13 of theelastomeric crown 4 to the second end face 14. Each of the plurality ofribs terminates at each end face 13, 14 of the elastomeric crown 4 witha bevelled or sloping surface 18 (the inner surface of the housing 62 onthe right side of FIG. 2 is omitted in the region of the rib 15 so as toshow the protruding surface 16 and the bevelled or sloping end. portions18). In this embodiment the upper surface of each of the plurality ofribs terminates in a flat surface 16. The flat surface is substantiallyparallel to a tangent 19 to the imaginary circular surface 20 of theelastomeric crown 4 formed at that point.

In the embodiment shown, each of the plurality of ribs extendsubstantially parallel to each of the plurality of passageways 11through the elastomeric crown 4, that is they also extend substantiallyparallel to the longitudinal axis 10 of the elastomeric crown 4. In thisembodiment, the mid-points of each of the flat surfaces 16 in thecircumferential direction and the axis 12 of the passageways 11 both liesubstantially on a common radial plane 50 passing through the axis 52 ofthe bearing 3 and bearing assembly 1.

The effect of the plurality of passageways 11 in the elastomeric crownon the contact pressure of the elastomeric crown 4 on the bearing 3 atthe inner surface of the elastomeric crown due to interference betweenthe elastomeric crown and the bearing is shown diagrammatically in FIG.3. A line 25 indicates pressure levels around the inner surface of theelastomeric crown, with a first point 26 corresponding to a minimumvalue of the pressure and a second point 27 corresponding to a maximumvalue of the pressure. The higher pressure field is located in front ofthe solid portions of the elastomeric crown 4 and the lower pressurefields are located in front of the plurality of passageways 11.

FIG. 4 shows diagrammatically the contact pressure at the outer surfaceof the elastomeric crown due to interference between the outer surfaceof the elastomeric crown 4 and the inner surface of a housing (notshown). This Figure illustrates the effect of the plurality of ribs onthis contact pressure. The level of contact pressure is represented by aline 30 on which a first point 31 represents a minimum contact pressureand a second point 32 represents a maximum contact pressure. The higherpressure fields are located in the region of each of the plurality ofribs 15 and the lower pressure fields are located in the regions betweeneach of the plurality of ribs. It is the purpose of the ribs 15 toreduce the effects caused by any imperfections in the inner surface ofthe housing.

When the effects illustrated in FIGS. 3 and 4 are combined, it will beunderstood that the pressure variations introduced by the plurality ofpassageways 11 through the elastomeric crown 4 are partially offset bythe plurality of ribs 15.

Thus, while providing sufficient force to act to close the axial split,the elastomeric crown decreases the stress level in the bearing to avoidor substantially eliminate the occurrence of undesirable creep bendingin the elastomeric crown. Also, the variations between a minimum and amaximum pressure level will tend to reduce the effect of imperfectionsin the inside surface of the housing on the performance of the bearingassembly.

Other numbers of passageways 11 in the elastomeric crown 4 are alsopossible; for example an elastomeric crown can be produced with aplurality of passageways comprising six passageways, and a plurality ofribs comprising six ribs. The effect in the contact pressures at theinner and outer surfaces if the elastomeric crown in such an embodimentcan be seen in FIGS. 5 and 6.

In FIG. 5, a line 35 represents the contact pressure at the innersurface of the elastomeric crown due to the interference fit, on which afirst point 36 represents a minimum contact pressure and a second point37 represents a maximum contact pressure. It will be seen that thedifference between the minimum contact pressure and the maximum contactpressure is greater in this embodiment than in the previous embodiment.

In FIG. 6, a line 40 represents the contact pressure at the outersurface of the elastomeric crown due to the interference fit, on which afirst point 41 represents a maximum contact pressure and the points 42represent minimum contact pressures. It can be seen in such anembodiment in which the arcuate portions of the crown containing one ofthe plurality of passageways are evenly distributed with those arcuateportions of the crown not containing one of the plurality ofpassageways, that the plurality of ribs are not able to fully tocompensate for the effect of the plurality of passageways. Inparticular, it can be seen that the maximum contact pressure levels atthe outer surface of the elastomeric crown correspond to thecircumferentially outermost parts of each of the flat-topped ribs, andthat a reduced pressure level exists between the edges of each of theribs. While this embodiment gives adequate performance, the previousembodiment is to be preferred because of the lower difference betweenthe minimum and maximum pressure fields, and because of the loweroverall stress levels generated in the elastomeric crown. The reductionof the gap between the minimum and maximum pressure levels is desirablesince the variation between the two leads to variations in the rotatingtorque value. It has been found that in use the first embodiment allowslow torque variations of the steering column axis.

What is claimed is:
 1. A bearing assembly comprising a cylindricalbearing having an axial split and an elastomeric crown located about thesplit bearing, the elastomeric crown including an elastomeric cylinderhaving an annular wall about a longitudinal axis, a plurality ofpassageways extending longitudinally through the cylinder wall, and aplurality of ribs extending along an outer surface of the elastomericelement, the cylindrical bearing including two flanges that embrace aninner portion of the elastomeric crown.
 2. A bearing assembly accordingto claim 1, wherein the cylindrical bearing operates without clearanceagainst a co-operating shaft.
 3. A bearing assembly according to claim1, wherein the inner surface of the bearing is lined with ananti-friction material.
 4. A bearing assembly comprising a cylindricalbearing having an axial split and an elastomeric crown located about thesplit bearing, wherein the cylindrical bearing is a flanged bush.
 5. Abearing assembly according to claim 4, wherein the cylindrical bearingoperates without clearance against a co-operating shaft.
 6. A bearingassembly according to claim 4, wherein the inner surface of the bearingis lined with an anti-friction material.
 7. A bearing assembly accordingto claim 4, wherein the elastomeric crown comprises an elastomericcylinder having an annular wall about a longitudinal axis, a pluralityof passageways extending longitudinally through the cylinder wall, and aplurality of ribs extending along an outer surface of the elastomericelement.
 8. A bearing assembly according to claim 7, wherein thepassageways extend substantially parallel to the longitudinal axis ofthe elastomeric element.
 9. A bearing assembly according to claim 7,wherein the plurality of ribs extend substantially parallel to thelongitudinal axis of the elastomeric element.
 10. A bearing assemblyaccording to claim 7, wherein the plurality of ribs are located radiallyoutwardly of the passageways.
 11. A bearing assembly according to claim7, wherein at least one rib comprises a bead extending longitudinallyalong the elastomeric cylinder, said bead projecting from the outersurface of the elastomeric cylinder, the outer surface of the bead beinga flat formed parallel to a tangent of the outer surface of theelastomeric cylinder.
 12. A bearing assembly according to claim 7,wherein the passageways are of circular cross section.
 13. Anelastomeric crown for a bearing assembly comprising an elastomericcylinder having an annular wall about a longitudinal axis, a pluralityof passageways extending longitudinally through the cylinder wall, and aplurality of ribs extending along an outer surface of the elastomericelement.
 14. An elastomeric crown according to claim 13, wherein thepassageways extend substantially parallel to the longitudinal axis ofthe elastomeric element.
 15. An elastomeric crown according to claim 13,wherein the plurality of ribs extend substantially parallel to thelongitudinal axis of the elastomeric element.
 16. An elastomeric crownaccording to claim 13, wherein the plurality of ribs are locatedradially outwardly of the passageways.
 17. An elastomeric crownaccording to claim 13, wherein at least one rib comprises a beadextending longitudinally along the elastomeric cylinder, the beadprojecting from the outer surface of the elastomeric cylinder, the outersurface of the bead being a flat formed parallel to a tangent of theouter surface of the elastomeric cylinder.
 18. An elastomeric crownaccording to claim 13, wherein the passageways are of circular crosssection.
 19. An elastomeric crown according to claim 13, wherein amid-point of the ribs in the circumferential direction is contained in aradially directed plane which also includes the axis of a passageway.20. An elastomeric crown according to claim 13, wherein the passagewaysare located circumferentially equidistantly from one another.